Gas turbines comprise a compressor for compressing air, a combustor for producing a hot gas by mixing fuel and air and burning the resulting mixture, and a turbine to extract work from the expanding hot gas produced by the combustor. Gas turbine compressors pressurize inlet air which is then reverse flowed to the combustor where it is used to provide air to the combustion process. Each combustion chamber assembly comprises a cylindrical combustor liner, a fuel injection system, and a transition piece that guides the flow of the hot air from the combustor liner to the entrance of the turbine section.
Gas turbines are known to emit various undesirable oxides, such as nitrogen oxide (NOx), carbon monoxide (CO), as well as unburned hydrocarbons. It is well known that both oxidation of molecular nitrogen and oxidation of carbon monoxide to carbon dioxide depend on the temperature of the hot gas which is produced inside the turbine combustor and then flows through the transition piece to the turbine section. In addition, the residence time of the reactants in the combustor at these high temperatures is also a factor in producing undesirable emissions. To improve the performance of the combustor with respect to emissions, gas temperatures have to be high enough for an adequate period of time to oxidize carbon monoxide without being so high that excessive amounts of nitrogen oxides are produced.
Existing dry low NOx combustors (DLN combustors) minimize the generation of NOx, CO and other pollutants. These DLN combustors provide a fuel-lean mixture of fuel and air prior to combustion. Dilution air is provided to the combustor liner to absorb heat and reduce the temperature rise to a level where thermal NOx is not formed. Dilution air may also be provided to the transition piece between the combustor and the first stage nozzle. However, in many cases, even combustors with lean premixed fuel and air still achieve sufficiently high temperatures to produce undesirable emissions.
NOx emissions requirements are becoming more stringent Accordingly, there is a need for a lower NOx emission combustor that utilizes various ways to control the influx and movement of air in the combustor as well as to effect independent and variable control of fuel flow to fuel introduction locations of the combustor.